Bitcoin is back: Price quietly jumps 80%

Bitcoin, the controversial cryptocurrency, finally may be back in investors' good graces: It's up more than 80 percent from its April lows on a wave of good news and wider acceptance.

"Recently more and more people are realizing how much of a world-changing technology bitcoin is," Roger Ver, the bitcoin investor sometimes known as "Bitcoin Jesus," wrote in an email to CNBC. "We will see more and more of this until each bitcoin is at least tens of thousands of dollars each. I think this will happen sooner than any of us expect."

The price of a bitcoin hit a low of $360 in April and had been hovering around $450 since April 25. But it started breaking away on May 20. It now sits at $665, according to CoinDesk.

The exact reason for this move is hard to pin down. The Bitcoin2014 Conference in Amsterdam drew to a close three days before the upswing started, and it featured some positive outlooks for the cryptocurrency from its 2,000 attendees.

"The fact that you have 51 countries (represented at the conference) and all of them have something positive to say about developments in their countries—maybe this helped show that bitcoin is bigger than just the U.S., China and England," said Micky Malka, a general partner at venture capital firm Ribbit Capital and a board member of conference host Bitcoin Foundation.

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Malka said he has seen an increased interest in bitcoin over the past few months in the Silicon Valley venture capital community. An average round of funding for a bitcoin-related company drew in $1 million or $2 million in 2013, he said, but now routinely exceeds $20 million.

"(There is) momentum of serious committed entrepreneurs diving into building something with this technology," he said. "Venture investors are backing them and really starting to believe we can improve people's lives."

To be sure, bitcoin still receives its share of bad press. Earlier Tuesday, Erik Voorhees, the co-owner of two bitcoin-related sites, agreed to pay the U.S. Securities and Exchange Commission roughly $51,000 to settle charges that he illegally offered shares of unregistered ventures.

And earlier this year, Manhattan federal prosecutors subpoenaed several bitcoin exchanges as part of an investigation into illegal online transactions.

Whatever the reason for it, though, the recent swing to the upside only begins to make up for lost ground since bitcoin's December highs above $1,100.